Implement native runout animation attributes and reproduce the missing biped transition

docs/RUNOUT.md

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+# Runout crash investigation
+
+The Hardcore 360-flip reports at ticks 583 and 378 terminate at MotionGraph
+behavior 86, `AddRunoutAttribs`. This operation was unsupported before the
+difficulty-menu changes. Entering the stock runout graph now succeeds in Easy,
+Normal and Hardcore. A full-frame regression then exposed the next missing
+owner: `PhysicsGround -> BipedGround` has no production adapter yet.
+
+## Reference
+
+TU3 dump `default_82000000_011B0000.bin`, guest base 0x82000000,
+SHA256 f4aa113eb541bfba03dbc108cf5ab43f58c965b20fa3b82f9c40938a0ad841c4.
+Registration 0x82F89700 selects factory 0x82BC9BA8; vtable 0x82320BDC has
+Begin 0x82BBA4A8, Update 0x82BBA770 and empty End 0x82B61BB8.
+The initializer pair 0x82F85870/0x82F85888 identifies BipedStartAngle/BipedSpeed.
+Addresses are guest addresses; subtract 0x82000000 for dump offsets.
+
+Observed: Begin reads Skeleton0 (effective animation root Z),
+SystemReckoning16 (COM velocity), SystemReckoning96 (up), and mirrors through
+ISkaterAnim slot28. OffBoard331 selects alternate velocity OffBoard128.
+It uses 0x8286CD88 for the projected signed angle, wraps with the strict
+fraction > 0.5 condition, converts radians to degrees using word 0x42652EE1,
+and captures full three-dimensional speed. Update emits the retained values
+with normalized=false and sequence=-1. End performs no writes.
+
+The game currently publishes the ordinary velocity branch; existing riding/air
+states leave OffBoard331 at its native reset value. The alternate branch is
+implemented and tested but requires the future BipedAir output owner.
+
+The host numerical routines follow recovered arithmetic; no hardware-matched
+360-flip replay has been recorded. A test-injected runout request verifies the
+stock animation branch in all three modes, not complete on-foot physics.
+
+## Remaining integration
+
+User explicitly selected implementing native on-foot/runout instead of an
+error-recovery screen. BipedGround requires the contact toolkit (82D811C8 /
+82D81610), ground job producer, controller placement/update, skeleton mode4,
+board manager, state publications, and BipedAir/remount transitions. Existing
+recovered modules are being compiled and connected; enabling modules alone is
+not a working BipedGround implementation.